Fact of the Day #105
It’s mentioned a few times early on in the series that a true Philosopher’s Stone would never break or run out, hence why Ed thought Cornello’s Stone was fake. Dr. Marcoh confirms that all Stones created using his method, including the ones used during the Ishvalan War, are imperfect prototypes and not true Philosopher’s Stones.
That’s right, kids… After all Ed and Al’s work to crack the code, every single Philosopher’s Stone shown in the series, including Father and Hohenheim, is a fake.
(Source: Chapters 2 and 8; Also, thanks to @froborr for pointing this out at a convention panel.)